Genome of Rickettsia endosymbiont suggests candidate mechanisms for fitness benefit to invasive whitefly host

Facultative bacterial endosymbionts can move in and out of their arthropod host populations within an ecological time scale, bringing new sets of genetic capabilities that may permit host adaptation to different conditions, affecting host population structure and drive host evolution. Bemisia tabaci is a species complex of insect pests of agricultural systems, within which the invasive species provisionally known as “B” or “MEAM1” may house a Rickettsia endosymbiont. Different host relationships have been reported for this symbiont among locations, with Rickettsia providing strong fitness benefits to some populations of whiteflies in the USA. Here we tested the hypothesis that this benefit was due to a nutritional supplement provided by Rickettsia to the whitefly host, which feed on a limited diet of plant phloem. We compared the genomic sequence of the mutualist whitefly Rickettsia to related Rickettsia from other arthropod hosts. We found limited genomic evidence to support this hypothesis but suggest alternative hypotheses arising from the genomic data about what mechanism may underlie the fitness benefit. These results help to interpret the complex interaction between Rickettsia and whiteflies.